首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   513331篇
  免费   10055篇
  国内免费   4976篇
化学   272644篇
晶体学   8167篇
力学   23740篇
综合类   257篇
数学   58719篇
物理学   164835篇
  2022年   4254篇
  2021年   5495篇
  2020年   5923篇
  2019年   6392篇
  2018年   7806篇
  2017年   7972篇
  2016年   11345篇
  2015年   7323篇
  2014年   11400篇
  2013年   24934篇
  2012年   20121篇
  2011年   23500篇
  2010年   16987篇
  2009年   16761篇
  2008年   20352篇
  2007年   19954篇
  2006年   18582篇
  2005年   16277篇
  2004年   14969篇
  2003年   13226篇
  2002年   12956篇
  2001年   15058篇
  2000年   11464篇
  1999年   9160篇
  1998年   7593篇
  1997年   7370篇
  1996年   7062篇
  1995年   6294篇
  1994年   6085篇
  1993年   5728篇
  1992年   6613篇
  1991年   6655篇
  1990年   6350篇
  1989年   6267篇
  1988年   6003篇
  1987年   6105篇
  1986年   5698篇
  1985年   7275篇
  1984年   7308篇
  1983年   5954篇
  1982年   6117篇
  1981年   5915篇
  1980年   5618篇
  1979年   6137篇
  1978年   6168篇
  1977年   6261篇
  1976年   6109篇
  1975年   5691篇
  1974年   5559篇
  1973年   5592篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
The problem of the vector and axial-vector dominance of weak interactions within the framework of the quark model of superconductivity type is discussed.  相似文献   
22.
23.
24.
25.
We consider the growth of a spherical crystal in a supersaturatedsolution. In the first part, existence and uniqueness resultsfor radially symmetric growth are obtained, provided that thesupersaturation is not too large; conversely, when the far-fieldsupersaturation exceeds a critical value, it is shown that theradially symmetric solution ceases to exist in finite time.In the second part, we examine the linear stability of a radiallysymmetric similarity solution (in which the radius grows ast?) to shape perturbations. The results are compared with previousquasi-static analyses, and, in particular, the critical radiusat which the crystal becomes unstable is found to be largerfor small supersaturations, but smaller for large supersaturations,than those predicted by the quasi-static analysis  相似文献   
26.
27.
Using the method of the tensor Green’s function of the wave equation, the differential and total cross sections for the scattering of surface optical electromagnetic waves (surface plasmon polaritons) by a spherical nanoparticle into surface plasmon polaritons and light have been obtained with the inclusion of the magnetic dipole contribution. Using the example of noble metal systems, it has been shown that the magnetic dipole contribution may significantly affect the angular dependence of the differential cross sections and increase their anisotropy as the plasmon wavelength increases.  相似文献   
28.
Dielectric properties of polymer-liquid crystal mixture, having constituent polymer, poly-butyl methacrylate (PBMA) and liquid crystal, cholesteryl nonanoate, are reported as a function of frequency and temperature. The measurement has been done in a temperature range of 300-375 K and frequency range of 100 Hz-10 MHz. The dielectric permittivity and dielectric loss shows significant changes with the addition of polymer molecules in liquid crystal. The significant feature of composite formation is that the pure liquid crystal and polymer do not show dielectric relaxation in the frequency range covered, while the composite shows relaxation peak at a particular frequency. The optical transmittance of pure liquid crystal and composite has also been measured and compared.  相似文献   
29.
We report morphologic changes of metallic surfaces at the onset of ablation, starting from gentle ablation to the emergence of ablation craters. The evolution of both observed melting zones and of ablation craters therein are investigated in dependence of the ablation laser fluence for nanosecond ultraviolet laser pulses. Further, consequences of crater formation for cluster synthesis within the released atomic vapor are pointed out. PACS 52.38.Mf; 79.20.Ds; 65.40.De  相似文献   
30.
A new solvent-free sample preparation method using silver trifluoroacetate (AgTFA) was developed for the analysis of low molecular weight paraffins and microcrystalline waxes by laser desorption/ionization time-of-flight mass spectrometry (LDI-TOFMS). Experiments show that spectral quality can be enhanced by dispersing AgTFA directly in liquid paraffins without the use of additional solvents. This preparation mixture is applied directly to the MALDI probe. Solid waxes could be examined by melting prior to analysis. The method also provides sufficiently reproducible spectra that peak area ratios between mono- and bicyclic alkane peaks indicated variations in the cycloalkane content of paraffin samples. Dehydrogenation of hydrocarbons observed during the desorption/ionization process was studied by analysis of alkane standards.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号